1. Field of the Invention
The present invention relates to an internal antenna, and more particularly to an internal antenna with a small-sized structure usable in a multiple band.
2. Description of the Related Art
Typically, helical antennas or linear monopole antennas are used as antennas for potable terminals. However, although these helical antennas or linear monopole antennas have a merit of omni-directional radiation characteristic, since they are of external type projecting outside the terminals, there is a fear of breakage of antennas and their characteristic deterioration due to an external force. Also, they are vulnerable to recently proposed SAR (Specific Absorption Rate).
A portable terminal antenna for a mobile communication are facing with a user's need for good design, convenience of carrying, service commercial use in a multi-band, light-weighting, and low cost. Accordingly, the portable terminal antenna for the mobile communication requires an internal type of the multi-band including an 800 MHz band rather than an external type and are meeting a need for miniaturization using a variety of structures and a variety of materials.
A conventional internal antenna includes a microstrip patch antenna, a planar inverted F antenna, a chip antenna, etc. There have been proposed many methods for effectively miniaturizing these internal antennas. For example, there is a case where a size of the microstrip patch antenna having a relatively high gain and a wideband characteristic is reduced using an aperture coupled feed structure. This provides a miniaturized and light-weighted antenna where a size of the antenna is effectively reduced by inserting a dielectric under an edge portion of a patch with the largest electric field distribution of a TM01 mode of the microstrip patch antenna in a longitudinal direction of a resonance patch and a gain reduction of the antenna produced as the dielectric constant is raised is minimized. However, since the miniaturization method used in the conventional antenna is based on a two-dimensional structure, there is a limit to the miniaturization. Furthermore, considering a fact that a space for the antenna in the portable terminal gets reduced due to increase of portable terminal services, there is a keen need of improvement for the miniaturization.
In addition, although a feeding system used in the conventional antenna includes an inverted L type, an inverted F type, etc., there is still a need of improvement in view of a space use or a feeding efficiency.